High integrity hanger and seal for casing

ABSTRACT

Casing segments and an expansion cone are positioned and cemented within a new section of a wellbore with a lower casing segment in an overlapping relationship with an upper casing segment. The lower casing segment is radially expanded such that an upper end of the lower casing segment comes into contact with the interior wall of the upper casing segment at the overlap region. The upper casing segment has an inward facing profile at the overlap region that includes a set of wickers that are driven into the lower casing exterior when it is expanded. This forms a metal-to-metal seal between the upper and lower casing segments at the overlap region.

FIELD OF THE INVENTION

This invention relates in general to wellbore casing or liner and in particular to a high integrity hanger and seal used in casing while drilling operations.

BACKGROUND OF THE INVENTION

In conventional well drilling, several casings 12, 14 are installed in the well borehole 10 to maintain the integrity of the borehole wall, as shown in FIG. 1. The installed casing 12, 14 further prevents undesired flow of drilling fluid into the formation or flow of fluid from the formation into the borehole 10. An initial depth of the borehole 10 is drilled and a casing segment 12 is cemented in place. A subsequent casing 14, which is to be installed in a lower segment of the borehole 10, is lowered through the previously installed casing 12 of an upper borehole segment.

The casing 14 to be installed in a lower segment may be hung at the wellhead 16 as shown in FIG. 1. The casing 14 of the lower segment is of smaller diameter than the casing 12 of the upper segment to allow passage of the subsequently installed casing 14 through the casing 12 of the upper segment. Thus, the casings 12, 14 are in a nested arrangement with casing diameters decreasing in downward direction Annuli are formed between the outer surfaces of the casings 12, 14 and the borehole wall to seal the casings 12,14 from the borehole wall. Cement is introduced into the annuli to cement the casings in place. Due to this nested casing arrangement, a relatively large borehole diameter is required at the upper part of the wellbore. A large borehole diameter typically involves increased costs due to heavy casing handling equipment, large drill bits and increased volumes of drilling fluid and drill cuttings. Drilling rig time is involved due to required cement pumping, cement hardening, equipment changes due to large variations in hole diameters to be drilled, and the large volume of cuttings drilled and removed.

To try and remedy the issues with the nested casing arrangement, expandable tubulars have been employed for the sections of casing, or liner, below the upper section of casing. The subsequent expandable tubular is lowered into a portion of the well drilled out below the upper casing. Once in place, the tubular is expanded radially such that the bore diameter is approximately slightly less that of the upper casing. An overlap exists between the upper and lower casing segments that creates a seal between the segments when the tubular is expanded. However, due to well pressure and thermal growth, the seal may lose integrity.

A need exists for a technique that addresses one or more of the limitations of the existing procedures for forming new sections of casing in a wellbore. The following technique may solve these problems.

SUMMARY OF THE INVENTION

In an embodiment of the present technique, a casing may be comprised of a plurality of casing segments joined approximately end to end, with each casing segment comprising a wicker profile formed on the interior surface at one end of the casing segment. Once the casing segment is cemented in place within the well borehole, a subsequent casing segment having a smaller diameter than that of the cemented casing may be lowered on a drill string through the initial, cemented casing. The drill string may extend past the lower end of the subsequent, lower casing where a bottom hole assembly (“BHA”) is attached to the drill string. The BHA may comprise a drilling head and an underreamer. The drilling head and underreamer rotate during drilling operations to drill a desired length below the end of the initial casing segment. Once the drilling operation is complete, the BHA may be retrieved and the subsequent casing is cemented in place in a conventional manner such that a portion of the subsequent casing segment overlaps with the wicker profile of the initial, upper casing segment.

In an illustrated embodiment, a pig or expandable cone may then be run into the bore of the lower, subsequent casing on a string to radially expand the lower casing along its length. As the lower casing segment is radially expanded by the pig, the portion of the lower casing segment that overlaps with the wicker profile of the upper casing is deformed onto the wicker profile to form a metal-to-metal seal. The wicker profile bites into the exterior surface of the subsequent casing segment In addition to forming a high integrity metal to metal seal, the wicker mechanism can function as a casing hanger while the cement cures. The procedure described above may be repeated until the desired length of casing is installed.

The combination of the wicker profile, and the radial expansion of each subsequent casing segment to form a metal-to-metal seal against the wicker profile, improves sealing between casing segments while reducing the telescoping and borehole reduction effect.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a casing arrangement of the prior art.

FIG. 2 is a sectional view of joined casing segments, in accordance with an embodiment of the invention.

FIG. 3 is a sectional view of overlap or packoff region, in accordance with an embodiment of the invention.

FIG. 4 is a sectional view of a casing while drilling operation, in accordance with an embodiment of the invention.

FIG. 5 is a sectional view of a casing while drilling operation, in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 2, an embodiment of the invention shows a portion of a casing 20 is within a well borehole 24. Cement 22 is introduced into an annulus formed by the borehole 24 and the casing 20 to hold the casing 20 in place. In this embodiment, the casing 20 may be comprised of a plurality of segments, for example, an upper or initial casing or liner segment 28 is joined at one end with a lower or subsequent liner or casing segment 26. The term “liner” refers to casing that has its upper end a short distance above a previously installed string. A casing string normally extends to a wellhead at the surface. The terms “liner” and “casing” are used interchangeably herein.

An overlap region, tubular seal section, or packoff 32, shown in more detail in FIG. 3, exists at approximately where the segments 28, 26 are joined to each other after the lower casing segment 26 has been radially expanded. The upper casing segment 28 has an exterior surface 34 that is in contact with the cement 20 and also has an inner bore 30. Likewise, the lower casing segment 26 has an exterior surface 38 that is in contact with the cement 20 and has an inner bore 36. The inner bore 36 of the lower casing segment 26 has a diameter that is slightly smaller than the diameter of the inner bore 30 of the upper casing segment 28.

Referring to FIG. 3, an embodiment of the invention shows an enlarged illustration of the overlap region 32 in a set position, with the lower casing segment 26 radially expanded. In the set position, the exterior surface 38 of the lower casing segment 26 is sealingly engaged with a wicker profile 40 formed onto an interior end of the upper casing segment 28. Wickers 40 are not threads, but a series of small triangular-shaped, parallel grooves and ridges on the sealing surface. The wickers may have a depth ranging from 1/16″ to ⅛″. The wickers 40 are formed from metal and bite into the exterior surface 38 of the lower casing segment 26 to form a metal-to-metal seal to create a better seal than a smooth surface. Initially, the wicker profile 40 may also function as a hanger to support the weight of the lower casing 26 prior to the cement 20 curing around lower casing 26. Further, the interior of the overlap region 32 may comprise a set of grooves 42 above and below the wicker profile 40. The grooves 42 initially may allow a drill head to be located during casing while drilling operations. Once a drilling operation is completed, the grooves 42 may further function as pockets into which the lower casing segment 26 may extrude to thereby provide a secondary sealing function. Although a downward facing shoulder is shown, a shoulder is not necessary.

During casing operations as shown in FIGS. 4 and 5, the upper casing segment 28 may be lowered into the well borehole 24 and cased with cement 22 that is pumped through the bore of the upper casing 28 and back up the annulus in a conventional manner as taught by US 2007/0175665, hereinafter referenced in its entirety. If the upper casing segment 28 is the first segment then it may be hung from a hanger at the wellhead (not shown). As described in FIGS. 2 and 3, the overlap or packoff region 32 is formed on the lower, interior end of the upper casing segment 28.

The wellbore will be drilled deeper, either with a drill pipe string or by liner drilling. Continuing to refer to FIG. 4, the lower or subsequent casing segment 26 may be lowered into the well borehole 14 through the interior of the upper casing 28. In this embodiment, the lower casing segment 26 is suspended from a drill string 50 via a sub 52 attached to the drill string for liner drilling. That is, the well is being drilled while casing 26 is being run into the well. The sub 52 may be ported to allow for the flow of drilling mud and other fluid during drilling operations. The drill string 50 may extend through the sub 52 and past the lower end of the lower casing 26 where a bottom hole assembly (“BHA”) 60 is attached to the drill string 50. The BHA may comprise a drilling head 62 and a collapsible underreamer 64 that may radially extend beyond the exterior surface 38 of the lower casing segment 26. The drilling head 62 along with the underreamer 64 rotate during drilling operations to drill a desired length below the end of the upper casing segment 28. Once the desired drilled length is achieved, the underreamer 64 is collapsed and the BHA 60 may be retrieved.

As shown in FIG. 5, the lower casing segment 26 may be conventionally cemented, such as by reference to US 2007/0175665, and a pig or expandable cone 70 may then be run into the bore of the lower casing 26 on a string 72. The outer diameter of the pig 70 is expandable to be slightly larger than the bore of the lower casing segment 26 to allow the pig 70 to exert a force Fo (FIG. 3) to radially expand the lower segment 26 or at least an overlapping portion of lower segment 26. Pig 70 is normally lowered into lower casing 26, then radially expanded and pulled upward. Several techniques for expanding pig 70 are known in the art, such as in U.S. Pat. No. 7,195,061, for example. As the lower casing segment 26 is radially expanded by the pig 70, a portion of the lower casing segment 26 that overlaps with the overlap region 32 of the upper casing 28 is deformed onto the wicker profile 40 (FIG. 3) to form a metal-to-metal seal. The wicker profile 40 bites into the exterior surface 38 of the lower casing segment 26 that is within the overlap region 32 as previously shown in FIG. 3. The inner diameter of the overlapping portion of lower casing will be the same or approximately the same as the inner diameter of the non-overlapping portion of the upper casing 28. Optionally, the entire length of lower casing 26 could be expanded, rather than just the one overlapping portion. If the entire length is expanded, the resultant inner diameter will equal or nearly equal the inner diameter of upper casing 28.

The exterior surface 38 of the lower casing may be formed of a softer metal than that of the wickers 40 or wickers 40 may contain an inlay of soft metal. Further, the wickers 40 may be formed from a different type of metal that is harder than that of the rest of the upper casing 28, such as Inconel® 725. The yield strength of carbon steel casing is approximately 55 to 110 ksi, depending on the application. The wickers may have 120 ksi minimum yield strength and a hardness can vary between roughly less than 20 Rockwell C (“HRC”) to greater than roughly 37 HRC. The higher hardness of the wickers 40 ensures biting into the lower casing 28 overlap region. In addition, any portion of the lower casing segment 28 that remains above the overlap region 32 may be cut-off and removed, if desired. No additional sealing or pachoffs are required. The procedure described above may be repeated to install additional liner strings. Further, each metal-to-metal seal formed may be tested by pressurizing the interior of the casing and observing any drop in pressure.

While the invention has been shown in only one of its forms, it should be apparent to those skilled in the art that it is not so limited but is susceptible to various changes without departing from the scope of the invention. 

1. An apparatus for forming a wellbore casing in a well, comprising: an upper casing segment cemented within the well; a wicker profile formed at an interior end of the upper casing segment; a lower casing segment installed within the well; and an upper end on the lower casing segment that overlaps with and is radially deformed into the wicker profile on the upper casing segment, to create a metal-to-metal seal.
 2. The apparatus of claim 1, further comprising a circumferential recess formed adjacent to wicker profile on the interior of the initial casing segment, and a portion of the upper end of the lower casing segment is radially deformed into the recess.
 3. The apparatus of claim 2, wherein the wicker profile comprises a plurality of parallel, circumferential grooves, each of the grooves being triangular in configuration.
 4. The apparatus of claim 1, wherein after being radially deformed, the upper end of the lower casing segment has an inner diameter substantially equal to a nominal inner diameter of the upper casing segment.
 5. The apparatus of claim 1, further comprising an upper and a lower circumferential recess formed above and below the wicker profile on the interior of the initial casing segment, and a portion of the upper end of the lower casing segment is radially deformed into the recesses.
 6. The apparatus of claim 1, wherein a full length of the lower casing segment is radially expanded to a nominal inner diameter equal to a nominal inner diameter of the upper casing segment.
 7. The apparatus of claim 1, wherein an outer surface on the end of the lower casing segment is fabricated from a metal that is softer than the wicker profile.
 8. The apparatus of claim 1, wherein the wicker profile comprises a plurality of parallel, triangular shaped grooves, the grooves being fabricated of a harder metal than that of the upper casing segment, the wicker profile being joined to the upper casing segment.
 9. The apparatus of claim 1, wherein the upper casing segment is cemented within the well at the approximate location where the end on the subsequent casing segment overlaps with the wicker profile.
 10. An apparatus for forming a wellbore casing in a well, comprising: an upper casing segment cemented within the well; a wicker profile formed at an interior end of the upper casing segment, wherein the wicker profile comprises a plurality of parallel, circumferential grooves, each of the grooves being triangular in configuration, and wherein the grooves are fabricated of a harder metal than that of the upper casing segment, the wicker profile being joined to the upper casing segment; a lower casing segment installed within the well, wherein an outer surface on the end of the lower casing segment is fabricated from a metal that is softer than the wicker profile; and an upper end on the lower casing segment that overlaps with and is radially deformed into the wicker profile on the upper casing segment, to create a metal-to-metal seal.
 11. The seal assembly of claim 10, further comprising a circumferential recess formed adjacent to wicker profile on the interior of the initial casing segment, and a portion of the upper end of the lower casing segment is radially deformed into the recess.
 12. The apparatus of claim 10, wherein after being radially deformed, the upper end of the lower casing segment has an inner diameter substantially equal to a nominal inner diameter of the upper casing segment.
 13. The apparatus according to claim 10, further comprising an upper and a lower circumferential recess formed above and below the wicker profile on the interior of the initial casing segment, and a portion of the upper end of the lower casing segment is radially deformed into the recesses.
 14. The apparatus of claim 10, wherein a full length of the lower casing segment is radially expanded to a nominal inner diameter equal to a nominal inner diameter of the upper casing segment.
 15. The apparatus of claim 10, wherein the lower casing segment is cemented within the well at the approximate location where the end on the lower casing segment overlaps with the wicker profile.
 16. A method of creating a wellbore casing in a well, comprising: forming a wicker profile at an interior end of an upper casing segment; installing and cementing the upper casing segment in the wellbore; installing a lower casing segment at a lower depth than the upper casing segment so that an end of the lower casing segment overlaps with the wicker profile on the upper casing segment; and radially expanding at least a portion of the subsequent casing segment to create a metal-to-metal seal between the upper and lower casing segments at the point where the upper and lower casing segments overlap.
 17. The method of claim 16, further comprising the steps of: drilling a predetermined depth below the end of the upper casing to create an open hole that accommodates the lower casing segment; cementing the lowert casing segment prior to radially expanding the lower casing segment; and pressurizing the bore of the casing to test for leakage at the metal-to-metal seal.
 18. The method of claim 16, wherein radially expanding at least a portion of the lower casing segment is by an expansion tool.
 19. The method of claim of 16, wherein forming a wicker profile comprises forming the wicker profile of a harder metal than a metal of the upper end of the lower casing segment. 